This invention relates to a method of improving the control behavior of an ABS control system and more particularly for improving the steerability of the vehicle and the driving stability during cornering, wherein a vehicle reference speed is derived and criteria for identifying a cornering situation and the direction of cornering are obtained from the rotational behavior of the vehicle wheels wherein, instead of the standard control mode, a special control mode or rather a corner control mode comes into operation when a cornering situation is identified, said special control mode or corner control mode producing a reduction of the braking pressure on the front wheel and/or on the rear wheel on the inside of the curve.
In a cornering identification system, with a method of control of the type presently mentioned, the pressure relief of the wheels on the inside of the curve generates a yawing moment around the vertical axis of the vehicle which balances and stabilizes the cornering situation. With control coming on during a partial braking operation, the braking pressure on the wheels on the outside of the curve will be kept constant or will automatically increase due to the cut-off of any further build-up of braking pressure on the wheel or wheels on the inside of the curve.
From DE 34 13 738 C2 (P 5547) there is already known an anti-lock control system (ABS) with a cornering identification circuit likewise based on wheel slip measurement. For the purpose of identifying a cornering situation, the slip values of the wheels of one vehicle side are added up and compared with the slip sum of the wheels of the other vehicle side and a cornering identification signal will be generated as soon as the difference between the slip sums exceeds a predetermined limit value. Selection criteria such as "select low" or "select high" criteria, according to which the pressure variation is controlled in the individual braking pressure control channels of this brake system, and limit values for the coming-on of these selection criteria will be varied when a cornering situation is identified. In this way, control is to be adapted to the varying conditions during driving straight onwards and during cornering.
It is known from older DE 21 19 590 A1 to obtain a cornering identification signal by means of a transverse acceleration measuring device such as a mercury switch.
It is further already known to expand the functions of an ABS control system in that the system is used for improving the driving and braking stabilities in corners. This is done in that a stabilizing moment is generated around the vertical axis of the vehicle by means of a calculated deceleration of the build-up of the braking pressure on the wheels on the inside of the curve as compared with the braking pressure on the wheels on the outside of the curve during cornering and a partial braking operation, i.e. during a braking operation where ABS response threshold values are not reached ("Bremsanlage und Schlupf-Regelsystem der neuen 7er-Reihe von BMW", ATZ 97 (1995), pages 8-15; and "Bremsanlage und Schlupf-Regelungssysteme der neuen Baureihe 5 von BMW", ATZ 98 (1996), pages 188-194 ["Brake system and slip control system of BMW's new no. 7 line of models {ATZ auto journal, 97 (1995), pages 8-15}; and "Brake system and slip control systems of BMW's new no. 5 line of models" {ATZ auto journal, 98 (1996), pages 188-194}]). With no steering angle sensor being used, the information on the current steering angle is derived from the transverse acceleration which, on its part, is calculated from the wheel sensor signals.
It is thus an object of the present invention to develop a method of the type referred to above which will provide a marked contribution to improving the driving behavior and stabilization, respectively, of the vehicle by means of reliable cornering identification and reaction to this situation.